gchq/CyberChef · error · OperationError

Unable to decrypt using this key

Error message

Unable to decrypt using this key

What it means

Thrown by XXTEADecrypt.run when the underlying decrypt(new Uint8Array(input), key) raises any exception. The catch is broad: it collapses every failure (wrong key, malformed ciphertext, incorrect block structure) into the single message 'Unable to decrypt using this key', discarding the original error detail.

Source

Thrown at src/core/operations/XXTEADecrypt.mjs:51

                "name": "Key",
                "type": "toggleString",
                "value": "",
                "toggleValues": ["Hex", "UTF8", "Latin1", "Base64"]
            },
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        const key = new Uint8Array(Utils.convertToByteArray(args[0].string, args[0].option));
        try {
            return decrypt(new Uint8Array(input), key).buffer;
        } catch (err) {
            throw new OperationError("Unable to decrypt using this key");
        }
    }

}

export default XXTEADecrypt;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Confirm the key is the exact key used to encrypt.
2. Ensure the input is the raw XXTEA ciphertext bytes (ArrayBuffer) with no headers/padding; convert via the correct input type.
3. Check that the byte length is a positive multiple of 4 (XXTEA word size).
4. If you only have the cipher text and do not know the variant, this error alone cannot distinguish wrong-key from malformed-input — try the original key/format first.

Example fix

// before: input is hex string, not converted to bytes
chef.bake(hexCiphertext, [{op:"XXTEA Decrypt", args:[{string:key,option:"Hex"}]}]);
// after: convert hex to bytes first, then decrypt
chef.bake(hexCiphertext,
  [{op:"From Hex"}, {op:"XXTEA Decrypt", args:[{string:key,option:"Hex"}]}]);

function isValidXxteaInput(bytes, key) {
  if (!(bytes.byteLength > 0 && bytes.byteLength % 4 === 0)) return false;
  if (key.length !== 16) return false; // typical XXTEA key constraint
  return true;
}

const isXxteaWordAligned = (ab) => ab.byteLength > 0 && ab.byteLength % 4 === 0;

try { result = chef.bake(input, [{op:"From Hex"},{op:"XXTEA Decrypt",args:[...]}]); } catch (e) { if (/Unable to decrypt using this key/.test(e.message)) { /* wrong key or malformed ciphertext */ } else throw e; }

When it happens

Trigger: The input is not a valid XXTEA-encrypted byte stream for the supplied key, or the key/input length violates XXTEA constraints (XXTEA operates on a 32-bit-word array; an input whose byte length is not a multiple of 4, or is too short, can fail).

Common situations: Wrong key; ciphertext truncated or prepended with extra bytes (header, IV); input not first converted to the right byte format; decrypting data that was encrypted with a different XXTEA variant.

Related errors

• Invalid PKCS#5 padding.
• Invalid BIT padding.
• ${err}
• Letter ${letter} is not included in LS47
• No padding requested but input is not a ${blockSize}-byte mu

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/f2a6ba559b54ea88. Report an issue: GitHub.